“The most conservative justices on our nation’s High Court have once again sided not with hard-working Americans but this time with the wealthiest of political contributors. As a result, some of our government offices and public policies could end up being bought by the highest bidder.”

WASHINGTON — The Supreme Court on Wednesday issued a major campaign finance decision, striking down some limits on federal campaign contributions for the first time. The ruling, issued near the start of a campaign season, will change and most likely increase the already large role money plays in American politics.

The decision, by a 5-to-4 vote along ideological lines, with the court’s more conservative justices in the majority, was a sequel of sorts to Citizens United, the 2010 decision that struck down limits on independent campaign spending by corporations and unions. But that ruling did nothing to affect the other main form of campaign finance regulation: caps on direct contributions to candidates and political parties.

It did not affect familiar base limits on contributions from individuals to candidates, currently $2,600 per candidate in primary and general elections. But it said that overall limits of $48,600 by individuals every two years for contributions to all federal candidates violated the First Amendment, as did separate aggregate limits on contributions to political party committees, currently $74,600.

Chief Justice John G. Roberts Jr., writing for four justices in the controlling opinion, said the First Amendment required striking down the limits. “There is no right in our democracy more basic,” he wrote, “than the right to participate in electing our political leaders.”

Dissenting from the bench, Justice Stephen G. Breyer called the decision a blow to the First Amendment and American democracy. “If the court in Citizens United opened a door,” he said, “today’s decision may well open a floodgate.”

The decision chipped away at the central distinction drawn by the Supreme Court in its seminal 1976 campaign finance decision, Buckley v. Valeo. Independent spending, the court said in Buckley, is political speech protected by the First Amendment. But contributions may be capped, the court said then, in the name of preventing corruption. The court added that aggregate contribution limits were a “quite modest restraint upon protected political activity” that “serves to prevent evasion” of the base limits.

Wednesday’s decision concerned only contributions from individuals. Federal law continues to ban contributions by corporations and unions.

Led by Chief Justice Roberts, the court has been consistently hostile to campaign finance limits in its half-dozen decisions in argued cases on the subject so far. The five more conservative justices have voted together in all of those cases, though Chief Justice Roberts and Justice Samuel A. Alito Jr. have taken a more incremental approach than the bolder one called for by Justices Antonin Scalia, Clarence Thomas and Anthony M. Kennedy.

Wednesday’s decision may increase overall campaign spending, but it may also rechannel some of it away from “super PACs” and toward candidates and parties.